This invention relates to stabilizers for water-dispersed polymers, and more particularly to stabilizers for water-dispersed polymers that have a propensity to release acids and/or have groups that hydrolyze over time such as polychloroprenes and polyester urethanes.
Water dispersed polymers and polymer systems are widely available and are used, for example, as coatings and adhesives. Many of the known water-dispersed adhesive compositions contain polychloroprene. It is known that polychloroprenes and other similar halogenated compounds are not stable over time. Such compounds have a propensity to release acids over time in the form of halogens such as chlorides. This acid release lowers the pH of the system which can destabilize the polymer dispersion, detrimentally affect open time of an adhesive, and accelerate thermal degradation of the aqueous composition and the resulting waterless solid.
To solve the above problems, zinc oxide or a combination of zinc oxide and magnesium oxide have been used in compositions containing polychloroprene. These compounds are reported to function as acid scavengers and or crosslinkers. However, the use of these compounds in compositions containing polychloroprene has produced less than satisfactory results. For example, zinc oxide cannot be used with carboxylated polychloroprene dispersions because zinc ion will react with the organic acid groups and cause the polychloroprene dispersion to coagulate prematurely. It has also been reported that the presence of zinc oxide decreases the thermal stability of polychloroprene by lowering the temperature required for the polychloroprene to release labile chlorine. Additionally, compounds such as polyester urethanes may be prone to reaction with zinc oxide and are susceptible to acid induced hydrolysis of the polyester group if the free acid is not adequately scavenged. Thus, in some instances, the use of zinc oxide as an acid scavenger may limit the types of polymers which may be used in combination with polychloroprene. The addition of magnesium oxide to the above water dispersions containing zinc oxide does not solve the problem of premature coagulation of the dispersed polymers.
In one aspect, the invention provides a stabilizer system for polymers susceptible to hydrolysis and/or acid release comprising a combination selected from the group consisting of: branched primary amino alcohol and carbodiimide; branched primary amino alcohol and dihydroxy metal compound; carbodiimide and dihydroxy metal compound; carbodiimide, branched primary amino alcohol, and magnesium oxide; branched primary amino alcohol and magnesium oxide; carbodiimide and magnesium oxide; and a combination of branched primary amino alcohol, carbodiimide, and dihydroxy metal compound.
The stabilizing systems of the invention are free from zinc oxide, that is, do not contain zinc oxide. The stabilizing systems of the invention also do not contain aziridines and can also be used in dispersed polymers or solventless polymers without the need for external plasticizers. The term xe2x80x9cplasticizerxe2x80x9d, as used herein, means compounds from the following classes: phthalates including alkyl benzyl phthalates; adipates including dialkyl adipates; phosphates including alkyl aryl phosphates and triaryl phosphates; alkyl and aryl sulfonamides; and hydrogenated terphenyls.
The term xe2x80x9cacid scavengerxe2x80x9d means acid acceptor or acid neutralizer.
The term xe2x80x9cdispersionxe2x80x9d encompasses any form of solid dispersed in a liquid medium including, for example, latexes, emulsions, colloidal suspensions, and the like.
The stabilizer systems of the invention can be used in aqueous polymer dispersions and the resulting polymer after water has been removed to minimize a decrease in pH over time and/or minimize the hydrolysis of susceptible groups, for example, ester groups.
The stabilizer systems of the invention are useful for stabilizing polymers or polymer systems which contain ester groups or ester functionality or release acids upon aging. The polymers or polymer systems may be in the form of a water dispersion or may be the resulting solidified or dried adhesive after the water has been removed. Depending upon the mixture of components, the stabilizer systems of the invention protect the ester groups from hydrolysis and/or scavenge or neutralize free acid without the use of zinc oxide or plasticizers. The stabilizer systems of the invention comprise combinations of two or more components that may be used in polymers or polymer systems in an effective amount to minimize hydrolysis and/or free acid. As used herein, an xe2x80x9ceffective amountxe2x80x9d means a sufficient amount of a stabilizer system so to prevent either coagulation of the base polymer or hydrolysis of any ester moieties of the base polymer. A xe2x80x9cbase polymerxe2x80x9d is a polymer or combination of polymers that either coagulate or have ester moieties that hydrolyze, or both, in the presence of acid.
The stabilizer systems of the invention are typically useful in water-dispersed polymers or water-dispersed polymer systems containing halogenated species and/or ionic functionality, for example, carboxylation and/or sulfonation. The term xe2x80x9cwater dispersedxe2x80x9d means that the carrier is primarily water. However, incidental organic solvents, such as those present in additives and commercially available components, may be present. Preferably, however, xe2x80x9cwater-dispersedxe2x80x9d refers to a 100% water carrier. Examples of water-dispersed polymers that may require stabilization from hydrolysis or acid release include acrylics, acrylates, polyesters, polyurethanes, rosin esters, polychloroprenes, chlorinated polyolefins, polyvinyl chlorides, and combinations thereof. The stabilizer systems are also useful in the resulting adhesives that are formed from removing water from the above described polymers and polymer systems.
The stabilizer systems of the invention are generally used in compositions containing water-dispersed polymers which require stabilization in an effective amount. An xe2x80x9ceffective amountxe2x80x9d of a stabilizer system means an amount of stabilizer system so to prevent either coagulation of the polymer composition or hydrolysis of any ester moieties of the polymers or other resins containing ester moieties. Hydrolysis of ester moieties of the susceptible polymer will cause the adhesive performance of the adhesive prepared therefrom to decline. Such hydrolysis may be detected by a major shift in pH of the polymer system, for example, an adhesive composition, and by using analytical techniques such as Fourier Transform Infrared Spectroscopy (FTIR), Gas Chromatography (GC), and mass spectrometry.
The stabilizer systems of the invention may comprise one or more branched primary amino alcohols. The branched primary amino alcohols act primarily as an acid scavenger. The branched primary amino alcohols are derived from nitroparaffins by way of nitro alcohols. Useful branched primary amino alcohols are those which are miscible in water. Preferred primary amine alcohols include 2-amino-1-butanol; 2-amino-2-methyl-1,3-propanediol; 2-amino-2-methyl-1-propanol; 2-amino-2-ethyl-1,3-propanediol; and tris(hydroxymethyl)aminomethane.
The stabilizer systems of the invention may comprise one or more carbodiimides. A carbodiimide, as used herein, is a compound containing the functional group: xe2x80x94Nxe2x95x90Cxe2x95x90Nxe2x80x94. The carbodiimides are useful for preventing hydrolysis of functional groups such as ester groups. The carbodiimides may be aliphatic or aromatic. Useful carbodiimides are either miscible or dispersible in water. Preferred carbodiimides are those that are sterically hindered, water miscible, and contain little or no organic solvent. Preferred commercially available carbodiimides include Stabaxol(copyright) P 200 (reaction product of tetramethylxylene diisocyanate; water-dispersed), Stabaxol(copyright) P (poly(nitrilomethanetetraylnitrilo (2,4,6-tris(1-methylethyl)-1,3-phenylene)), and Stabaxol(copyright) I (tetraisopropyldiphenylcarbodiimide) (RheinChemie) and Ucarlnk(copyright) XL-29SE (Union Carbide). Both Stabaxol(copyright) P and I are useful in the compositions of the invention if first dispersed in water.
The stabilizer systems of the invention may contain one or more dihydroxy metal compounds. The dihydroxy metal compounds are useful as acid scavengers. Useful dihydroxy metal compounds are those compounds having fully substituted trivalent metal ion wherein two of the valences are filled with hydroxyl groups and the third valence is filled with a moiety other than hydroxyl. Useful dihydroxy metal compounds are dispersible in water. Preferred dihydroxy metal compounds include dihydroxyaluminum aminoacetate and dihydroxyaluminum sodium carbonate.
The stabilizer systems of the invention may also contain magnesium oxide. Preferably, the magnesium oxide is in the form of a water dispersion. It should be understood, however, that a certain amount of magnesium oxide converts to magnesium hydroxide in the presence of water. Preferred xe2x80x9cmagnesium oxidexe2x80x9d dispersions are made from commercially available magnesium oxide such as Elastomag(trademark) 170 (Morton Thiokol) and Maglite(trademark) A (C. P. Hall). Magnesium oxides may be dispersed by those skilled in the art or obtained from vendors such as Harwick Chemical, Tiarco Chemical, and H. M. Royal.
In general, branched primary amino alcohol may be used in a water-dispersed polymer or polymer system in an amount of from about 0.5 to about 5 parts per 100 parts dominant polymer by dry weight, hereinafter xe2x80x9cphr.xe2x80x9d As used herein, xe2x80x9cdominant polymerxe2x80x9d means the one polymer present in the highest concentration (on a dry basis) which requires stabilization, for example, that releases acid and/or has groups susceptible to hydrolysis over time. Preferably, the branched primary amino alcohol may be present in an amount of from about 2 to about 4 phr, more preferably from about 2.5 to about 3.5 phr. On a basis of parts by weight per 100 parts total dry solids by weight of a polymer system, the above ranges are about 0.5 to about 3 and about 1 to about 2.7, respectively.
Carbodiimide may be present in a water-dispersed polymer or polymer system in an amount of from about 0.5 to about 5 phr, preferably from about 2 to about 4 phr, more preferably from about 2.5 to about 3.5 phr. On a basis of parts by weight per 100 parts total dry solids by weight of a polymer system, the above ranges are about 0.25 to about 4, about 0.5 to 3.5, and about 1 to about 2.7, respectively.
Dihydroxy metal compound (as defined above) may be present in a water dispersed polymer or polymer system in an amount of from about 0.5 to about 5 phr, preferably from about 2 to about 4 phr, more preferably from about 2.5 to about 3.5 phr. On a basis of parts by weight per 100 parts total dry solids by weight of a polymer system, the above ranges are about 0.25 to about 3, about 0.5 to about 2, and about 0.8 to about 1.5, respectively.
Magnesium oxide may be present in a water dispersed polymer or polymer system in an amount of from about 0.5 to about 5 phr, preferably about 2.5 to about 3.5 phr. On a basis of parts by weight per 100 parts total dry solids by weight of a polymer system, the above ranges are about 0.25 to about 2 and about 0.5 to about 1.5, respectively.
Preferably, the above individual components are used in various combinations in a polymer or polymer system. Specific combinations of components are: a combination of branched primary amino alcohol and carbodiimide; a combination of branched primary amino alcohol and dihydroxy metal compound; a combination of carbodiimide and dihydroxy metal compound; a combination of branched primary amino alcohol, carbodiimide, and magnesium oxide; a combination of branched primary amino alcohol and magnesium oxide; a combination of carbodiimide and magnesium oxide; and a combination of branched primary amino alcohol, carbodiimide, and dihydroxy metal compound. Generally, the ratio of branched primary amino alcohol to carbodiimide ranges from about 0.5:1 to 1:0.5 by weight with a ratio of about 1:1 being preferred. A preferred ratio of branched primary amino alcohol to dihydroxy metal compound is about 1:1 by weight. A preferred combination containing magnesium oxide is the combination of branched primary amino alcohol, carbodiimide, and magnesium oxide in about 1:1:1 ratio by weight.
Combinations containing branched primary amino alcohol and dihydroxy metal compounds are preferred for acid scavenging applications. Combinations containing carbodiimide are preferred for hydrolysis prevention applications.
The stabilizer systems of the invention may optionally, but preferably, contain one or more antioxidants. Useful antioxidants include Octolite(trademark) 640, a 55% solids by weight emulsion blend 50:50 by weight of a polymeric hindered phenol and a thioester; Octolite(trademark) 561, a 50% solids by weight dispersion of 4,4xe2x80x2-butylidenebis(6-t-butyl-m-cresol); Octolite(trademark) 544, a 55% solids by weight dispersion of N,Nxe2x80x2-di-beta-napthyl-p-phenylenediamine; Octolite(trademark) 504, a 50% solids by weight dispersion of 2,2xe2x80x2-methylenebis(6-t-butyl-p-cresol); Octolite(trademark) 485 (a 46% solids by weight dispersion of Bisphenol antioxidant, an anionic emulsion of Uniroyal""s Naugawhite Liquid); Octolite(trademark) 424, a 63% solids by weight emulsion blend 50:50 by weight of a polymeric hindered phenol and di-tridecylthiodipropionate (DTDTDP) thioester; Octolite(trademark) AO-50, a 50% solids by weight emulsion of a hindered phenol and DTDTDP thioester; Octolite(trademark) AO-28, a 63% solids by weight emulsion blend 80:20 of a polymeric hindered phenol and DTDTDP thioether; and Octolite(trademark) WL, a 50% solids by weight emulsion of butylated reaction product of para-cresol and dicyclopentadiene, all available from Tiarco Chemical Division, Textile Rubber and Chemical Company, Inc., Dalton, Ga.
The stabilizer systems of the invention may be combined with polymers or polymeric systems as neat compounds or as water dispersions with mixing at room temperature. The components of the stabilizer system are typically added individually. Typically, the antioxidant(s), if present, is/are added first, followed by acid scavenger(s), followed by anti-hydrolysis agent(s), if used.
The stabilizer systems of the invention may be used to stabilize polymers or polymers systems containing, for example, polymers susceptible to hydrolysis and polymers that release groups that form acids. The specific combinations of the various individual components of the stabilizer system depends upon the type and characteristics of the polymers in the system. For example, in polymers or polymers systems that are susceptible to hydrolysis of ester groups and contain no acid generating polymers, such as carboxylated polyester polyurethanes, or sulfonated polyester polyurethanes, a combination of at least two of branched primary amino alcohol, dihydroxy metal compound, and carbodiimide would be used in an effective amount. Magnesium oxide would not be used in combination with other stabilizer components in polymers or polymer systems containing carboxylated polyester polyurethanes.
For compositions containing primarily acid generating polymers, for example, chlorine containing polymers, or combinations of acid generating polymers and sulfonated polyester polyurethanes, a combination of at least two of branched primary amino alcohol, carbodiimide, dihydroxy metal compound, and magnesium oxide, would be used in an effective amount with the exception of stabilizer systems containing both dihydroxy metal compound and magnesium oxide. In this case, the stabilizer system would also be used in an effective amount as defined in this application.